1. Field of the Invention
The present invention generally relates to a method and apparatus for optical interconnection and more particularly to a method and apparatus for optical interconnection in which an antenna is provided in a waveguide structure such that space and power are saved.
2. Description of the Related Art
Long-haul, high speed data communications are currently handled almost exclusively by fiber optic transmission systems. These systems operate at wavelengths of about 1.3 microns to about 1.56 microns, where silica waveguides are highly transparent, because minimizing the optical loss is a key engineering requirement in such systems.
Lasers and photodiodes at those wavelengths must be made of compound semiconductors such as indium-gallium arsenide (InGaAs) or the like. The expense and difficulty of using these materials is more than repaid by the huge bandwidths and inter-repeater distances they allow. Latencies in these networks are tens of milliseconds at least.
Shorter-range optical interconnection systems such as optical LANs and Fiber Channel disk array connections usually use 850 nm light, because at that wavelength ordinary gallium-aluminum arsenide lasers and silicon photodiodes are available at low cost, and fiber attenuation is not a major concern. Latencies here should be a few milliseconds at the most.
The shortest-range interconnections (e.g., on-chip and between-chip communications inside routers, computers, and other data-handling devices) are currently performed with metal wires in dielectric surroundings, which is cheap, highly dense, and well-proven.
However, as data rates increase, wiring will increasingly suffer loss, crosstalk, and drive power disadvantages. Thus, there is a general move underway to bringing optical interconnections to these small-scale applications, where their low loss, extreme bandwidth, potentially low power, and crosstalk-free operation will be of great value. However, the application is difficult for the optics since it requires high density, low cost, and extremely low latency (e.g., 100 picoseconds to a few nanoseconds).
The primary limiting factors on these short-range optical interconnections have been their high cost, large size, long latencies, and the drive power requirements of the current technologies. The root of these problems is that there have been no monolithically integrated optical interconnection technologies. That is, each one has required hybrid construction, to route the electrical logic signals through a laser driver, laser, waveguide, photodiode, and transimpedance amplifier chain. The optoelectronic components (e.g., vertical-cavity surface emitting lasers (VCSELs), InGaAs photodiodes, etc.) cannot be made in silicon, and the laser driver chip must provide a 2-V output swing, which a processor working from a single 1-V supply cannot do without ancillary circuitry such as a charge pump.
Further, as noted above, currently there is a separate laser or a separate modulator provided for each fiber or waveguide. Thus, for every single line, at least one component must be provided therefor on the board. Each of these components must be soldered or bonded on the board since lasers cannot be made of silicon. This is problematic due to space, cost, and yield detraction.
A further problem of hybrid construction is that the logic signal must be transmitted electrically between the logic output and the laser or modulator. If the laser or modulator is a separate chip, then this configuration requires the signal to be sent across an electrical transmission line on the module or circuit board, whose bandwidth and drive power requirements limit the benefit to be gained from the optical interconnection.
Hence, before the present invention, these disadvantages have prevented such optical technology from being applied to on-chip and between-chip interconnections.